High-flux small-pore zeolite membranes for biogas upgrading

Abstract

In recent years, the utilisation of biogas has attracted attention as an alternative to fossil fuels and as a countermeasure against global warming. Efficient utilisation of biogas requires biogas upgrading, and with technological advances, membrane separation using small-pore zeolite membranes with excellent molecular sieving effects is becoming mainstream. In this study, biogas separation was performed using a disc CHA membrane provided by ZeoMem, and a CO2 permeance recovery test was conducted using a used 50 cm DDR tubular membrane also provided by ZeoMem. For the CHA membrane, after measuring the initial performance using a single gas permeation setup, the separation performance evaluation of real biogas (30 L/min, feed pressure 10 bar) was carried out over 29 days. The biogas was used as received. In this long-term experiment, the temperature (25 ℃ to 200 ℃) and treatment conditions were changed stepwise to track the CO2 permeance and CO2/CH4 selectivity of the membrane. For the DDR membrane, after being contaminated by impurities in real biogas due to improper pretreatment at a company, its performance recovery was investigated using a single gas permeation setup. An 88-day experimental protocol consisting of eight different stages, including room temperature CO2 flushing (both dead-end and retentate-open) and subsequent thermal treatments under vacuum or N2 flow up to 200 ℃, were implemented to evaluate the membrane recovery. CO2 permeances for the DDR membrane were measured after each treatment stage. In addition, scanning electron microscope (SEM) and X-ray diffraction (XRD) were used for the structural observation of the membranes. In the biogas separation using the disc CHA membrane, the initial CO2 permeance was 47×10−7 mol/(m2·s·Pa) coupled with a CO2/CH4 selectivity of 241. The permeance decreased to 33 % of the initial value in 10 days at 25 ℃ due to fouling and the separation selectivity was also slightly decreased. However, by thermal regeneration at 60 ℃ to 200 ℃ under N2 flow, the CO2 permeance completely recovered on the 29th day to 47.6×10−7 mol/(m2·s·Pa), slightly exceeding the initial value, and the separation selectivity was also recovered. The results also suggest that certain pretreatments are needed to remove heavy components from real biogas before it is sent to the membrane unit. Regarding the performance recovery of the DDR membrane, the CO2 permeance was 11 % of the original one when it was taken back from the company, and it was recovered up to 69 % of the initial permeance after some simple treatments in this study. These experimental results indicated that small-pore zeolite membranes not only possess excellent biogas separation performance but can also be effectively regenerated from severe fouling through appropriate thermal and gas-flow treatments.

Popular Abstract

Recently, natural disasters such as severe summer heat and extreme precipitation from typhoons, continue unabated. Under these circumstances, the use of renewable energy sources such as hydropower, wind, solar, biomass, hydrogen, and biogas as eco-friendly alternatives to fossil fuels has become a global trend. Among these, the utilisation of biogas is drawing increasing attention. This is because reusing waste not only reduces the amount of waste incinerated and lowers environmental impact, but also generates energy for electricity and gas, thereby contributing to countermeasures against global warming. Biogas is a gas generated by microorganisms through the fermentation of livestock manure and food waste. It mainly consists of methane (CH4) and carbon dioxide (CO2). CH4 recovered through biogas upgrading can be used as an energy source. To efficiently utilise biogas for power generation or as fuel, biogas upgrading, which removes CO2 to increase the purity of CH4, is essential. Zeolites, porous aluminosilicate minerals containing countless nanoscale pores, can be utilised for this purpose. In this study, biogas upgrading experiments using zeolite membranes based on this principle were conducted. Two types of zeolite membranes, CHA and DDR, whose pore sizes are comparable to those of CO2 and CH4 molecules, were employed. Furthermore, CHA zeolite with a pore size of 0.38 nm is larger than the kinetic diameter of CO2 (0.33 nm) and similar to the kinetic diameter of CH4 (0.38 nm). Therefore, it can be used to separate CO2 from CH4. DDR zeolite has a pore size of 0.36 nm. The pore size is in between the kinetic diameter of CO2 and CH4. Therefore, it is also a suitable candidate for CO2/CH4 separation. The disc CHA zeolite membrane used to evaluate biogas separation performance, and the results demonstrated that the CHA membrane exhibits excellent performance and is highly suitable for biogas upgrading. For the tubular DDR zeolite membrane, experiments were conducted to investigate the membrane recovery methods after it was severely contaminated by dirty biogas, i.e. biogas full of compressor oil and many other impurities. The results revealed that heating the membrane combined with flushing an inert gas can recover the membrane to some extent. By demonstrating both high separation performance and an effective membrane recovery method, this thesis provides practical solutions for advancing biogas purification and contributes to the development of a more sustainable circular green energy economy.

• author: Morimoto, Natsuki
• supervisor: Liang Yu; Mariona Battestini Vives
• organization: Chemical Engineering (M.Sc.Eng.)
• course: METM01 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: membrane technology, zeolite membranes, high permeability, high selectivity, real biogas upgrading
• language: English
• id: 9247200
• date added to LUP: 2026-08-25 08:21:42
• date last changed: 2026-08-25 08:21:42